When updating the state-action value in the Monte Carlo method, is the return the same for each state-action pair?
The discussion uses poor notation, there should be a time index. You obtain a list of tuples $(s_t, a_t, r_t, s_{t+1})$ and then, for every visit MC, you update
$$Q(s_t, a_t) = Q(s_t, a_t) + \alpha (G_t - Q(s_t, a_t))\;;$$
where $G_t = \sum_{k=0}^\infty \gamma^k r_{t+k}$, for each $t$ in the episode. You can see that the returns for each time step are calculated for time timestep onwards, and so are not necessarily the same across time steps.